fix(tui): pad markdown table cells

[kitlangton]

What

Add one column of horizontal padding inside markdown table cells in the V2 TUI. Tables remain vertically compact, but borders no longer touch their content.

Before / After

Before: Grid tables used OpenTUI's default zero horizontal cell padding, so headings and body text sat directly against cell borders.

After: Assistant messages and compaction summaries pass cellPaddingX: 1, leaving one terminal column on each side of cell content without adding blank rows.

How

• Update both session-route markdown renderers in packages/tui/src/routes/session/index.tsx.
• Leave mini and mono table rendering unchanged so those intentionally compact surfaces retain their current layout.

Testing

• bun typecheck from packages/tui
• Repository pre-push typecheck, 32 packages successful
• bun run lint packages/tui/src/routes/session/index.tsx, 0 errors (existing warnings remain)
• OpenCode Drive scripted TUI capture using the simulated model and the production markdown renderer

Demo

The simulated response exercises a grid table in the modified V2 TUI: